IVO H. DAALDERis President of the Chicago Council on Global Affairs and served as U.S. Ambassador to NATO from 2009 to 2013. Follow him on Twitter @IvoHDaalder.

Many observers believe that the greatest damage Russia[1] has done to U.S. interests in recent years stems from the Kremlin’s interference in the 2016 U.S. presidential race. Although there is no question that Moscow’s meddling in American elections is deeply worrying, it is just one aspect of the threat Russia poses[2]. Under Vladimir Putin[3], Russia has embarked on a systematic challenge to the West. The goal is to weaken the bonds between Europe and the United States and among EU members, undermine NATO’s solidarity[4], and strengthen Russia’s strategic position in its immediate neighborhood and beyond. Putin wants nothing less than to return Russia to the center of global politics by challenging the primacy that the United States has enjoyed since the end of the Cold War. He has undertaken a major military modernization designed to intimidate neighbors and weaken NATO, and he has resorted to the overt use of military force to establish new facts on the ground—not just in what Moscow calls its “sphere of privileged interests,” which encompasses all of the former Soviet republics, but also further afield, including in the Middle East, an area where the U.S. military has long operated with a free hand.

For some time now, “the Kremlin has been de facto operating in a war mode,” the Russia scholar Dmitri Trenin[5] has observed, and Putin has been behaving like a wartime leader. Washington’s response to this challenge must be equally strong. First, it is critical to maintain transatlantic unity; divisions across the Atlantic and within Europe weaken NATO’s ability to respond to Russian provocations and provide openings for Moscow to extend its reach and influence. The alliance has responded to the new Russia challenge by enhancing its presence in eastern Europe and the Baltic states, and Russia has so far not threatened the territorial integrity of any NATO member state. But NATO must do more to bolster its deterrence by sending a clear message to